This invention relates to a process for the regeneration, by oxidation, of internal combustion engine emission particulates collected in filter traps associated with each of the engine cylinders or with groups of the engine cylinders.
Particulate emission control systems have been developed for diesel engines to reduce exhaust gas pollutants of internal combustion engines as much as possible. These systems include particulate filter traps which collect solid particulates, such as carbon. The known particulate filter traps, however, are not entirely free of problems since the particulates deposited in the filter may cause increased flow resistance in the engine exhaust system which in turn increases the exhaust back pressure on the engine. As the collected particulate mass increase, it leads to a higher fuel consumption, as a function of engine load and rpm, and may result in engine stall in extreme cases. It therefore becomes necessary to continuously or intermittently remove the deposited particulates in the filter trap, generally by oxidation.
Ceramic particulate filter traps of honeycomb structure, steel wool filter traps and ceramic foam filter traps, with or without catalytic coating, are proven effective particulate filter systems.
Oxidation of particulates collected in the filter trap commences at temperatures above 500.degree. to 550.degree. C. The required temperature for oxidation can be lowered to 400.degree. to 450.degree. C. by using catalytic coating. Diesel engines reach such high temperatures only at very high loads and speed ranges. Adequately frequent regeneration during the engine operating mode is therefore not assured. To raise the engine exhaust to the temperature required for oxidation, it has been known to throttle the air intake, throttle the exhaust gases or shift the fuel supply timing.
However, these approaches do not achieve high exhaust gas temperatures required for filter trap regeneration in the engine's lower load ranges. Besides, these known measures effect considerably higher engine fuel consumption.